Don't allow posting an empty comment

pkg/controller/comment/post_comment.go

@@ -131,6 +131,13 @@ func PostComment() http.HandlerFunc {
 		if r.Method == http.MethodPost {
 			// Default intent is preview unless told to submit.
 			if intent == "submit" {
+				// A message is required.
+				if message == "" {
+					session.FlashError(w, r, "A message is required for your comment.")
+					templates.Redirect(w, fromURL)
+					return
+				}
+
 				// Are we modifying an existing comment?
 				if comment != nil {
 					comment.Message = message

web/templates/photo/permalink.html

@@ -161,7 +161,8 @@
                         <label for="message">Add your comment</label>
                         <textarea class="textarea" cols="80" rows="4"
                             name="message" id="message"
-                            placeholder="Add your comment"></textarea>
+                            placeholder="Add your comment"
+                            required></textarea>
                         <p class="help">
                             Markdown formatting supported.
                         </p>